1. Field of the Invention
A stacker system, assembly and method for stacking printed materials, and more particularly, a stacking system, assembly and method that utilizes a drive control that permits driving at least one or a plurality of stacking supports at a precisely controlled first speed in a downward or descending direction and that permits free relatively uncontrolled movement in an ascending or upward direction.
2. Description of the Related Art
In the past, printing presses or other feeders would deliver printed materials in a shingled manner to a stacker that would stack the printed materials. The printed materials or products were, for example, journals, advertising brochures, newspapers, magazines and the like. The products were stacked in a stack, which contained sub-stacks that were displaced by 180°. The printed products usually had a fold, so a stacking of the printed products with a displacement of 180° was required so that the orientation and/or levelness of the stack is maintained even in higher product stacks. To perform such displacement, a rotary table was commonly used. The rotary table would receive a sub-stack and then be rotated approximately 180°, and then another sub-stack would be placed on top of the first sub-stack and so on, thereby maintaining the orientation and levelness of the stack relatively horizontal as the stack height grew.
The current designs for vertical movement of stacking grid units or compensating stackers, where two grid units are needed, in an upper stacking chamber of a stacker have either servo-controlled or vector-controlled motors. The servo-controlled or vector-controlled motor designs are expensive components and contribute to high manufacturing costs of the compensating stacker. These types of drivers are also slow and their machine failure recovery (i.e., the recovery time needed to move the grid units from a lower release position where the printed materials are released to the rotary table to an upper stacking position where they can begin receiving printed materials for stacking) is slow because the units were moved back into their home positions with the servo-motor for positioning referencing. These motors, while being accurate, are more expensive and difficult to maintain than other types of drivers, such as actuators or pneumatic cylinders. However, the other types of drivers are not as accurate and cannot be used where accurate control and speed are needed. Unfortunately, these other types of drivers, such as pneumatic actuators, do not accurately index at slow speeds which are required of conventional stackers which need to maintain a constant drop height and rate during a stacking process.
In some cross-stackers, the product flow, which is delivered in scale or shingled formation, is forwarded onto a first reception element or support in the form of a grating, through which a first sub-stack is formed. One or more of further gratings are arranged beneath this grating with all the gratings being stationary in the vertical direction. After the product stack, which is located on the upper grating, has reached a certain height, this grating, which is designed in two parts, is open, through which the product stack falls onto the grating lying below it. After a further height increase of the stack through the supply of printed products, this grating is also open through which the product stack falls onto a further grating or into a rotational basket or rotary table which rotates the stack located therein by 180° as mentioned earlier.
Another approach is illustrated in U.S. Pat. No. 6,149,149 which shows an alternating cross stacker for paper products that utilizes a first reception element on which paper products to be stacked are collected and a further reception element. Rotation devices were arranged beneath the reception elements. The reception elements were vertically displaceable such that the stack that is formed on the first reception element is transferred directly to the rotation device or rotary table with a very small fall height. To achieve this, the reception elements, which comprised a pair of opposing fingers or grates, of the lower reception unit would open after delivery of its sub-stack and the upper reception element would receive printed materials which would be stacked thereon and would descend through the opening between the first reception element or grates. The stack on the first reception element would then be delivered directly to the rotary table, while the grates of the second reception element would be moved above the first reception element, which is now below the second reception element, where it may begin receiving and stacking printed materials. This type of stacker was commonly referred to as an alternating stacker and U.S. Pat. No. 6,149,149 issued to Gammerler A G was typical of this type of stacker.
One drawback of the prior art stackers mentioned is they commonly used two motors with drives and required a close coupled connection of each grid section with a motor. This resulted in high costs because of the two motors, drives and the like.
What is needed, therefore, is a system, method and means for precisely controlling the driven movement, especially the downward driven movement, of the grid, finger units or product support.